1. Field
The present invention relates to alignment of transfer heads with a target substrate to facilitate transfer of micro devices.
2. Background Information
Integration and packaging issues are one of the main obstacles for the commercialization of micro devices such as radio frequency (RF) microelectromechanical systems (MEMS) microswitches, light-emitting diode (LED) display systems, and MEMS or quartz-based oscillators.
Traditional technologies for transferring devices include, e.g., “transfer printing”, which involves using a transfer wafer to pick up an array of devices from a donor wafer. The array of devices are then bonded to a receiving wafer before removing the transfer wafer. Some transfer printing process variations have been developed to selectively bond and de-bond a device during the transfer process. In both traditional and variations of the transfer printing technologies, the transfer wafer is de-bonded from a device after bonding the device to the receiving wafer. In addition, the entire transfer wafer with the array of devices is involved in the transfer process.
Linear encoders and rotary encoders can provide information about position or motion of mechanical system components. For example, optical linear encoders have been used in coordinate-measuring machines and can provide absolute reference signals for positioning. Traditionally, encoders have not been integrated within MEMS-scale devices, and where they have been used, the encoders do not detect rotational or positional alignment of the MEMS device components.